Electrode structure

Abstract

Provided is an electrode structure capable of suppressing variations in an effective region that functions as an electrode even if the accuracy of the range of formation of a catalyst layer is low. The outer peripheral edge of the porous transport layer (72) is positioned further inward than the outer peripheral edge of the first gas diffusion layer (62), the outer peripheral edge of the first catalyst layer (61), and the outer peripheral edge of the second catalyst layer (71). As a result, an effective region (A) of the first catalyst layer (61) and the second catalyst layer (71) can be defined by the porous transport layer (72). Therefore, even if the precision of the forming range of the first catalyst layer (61) and the second catalyst layer (71) is low, the deviation of the effective region (A) which functions as an electrode can be suppressed.

Description

Technical Field

[0001] The invention relates to an electrode structure. Background Art

[0002] In the past, it is known that there is a solid polymer water electrolysis device that produces hydrogen (H2) by electrolyzing water (H2O). The solid polymer water electrolysis device has a cell stack (cellstack) in which cell units (cells) and separators (seprators) are alternately stacked. Each cell unit has an electrolyte membrane and a catalyst layer formed on both sides of the electrolyte membrane. When using the solid polymer water electrolysis device, a voltage is applied between the catalyst layer on the anode side and the catalyst layer on the cathode side, and water is supplied to the catalyst layer on the anode side. As a result, the following electrochemical reaction occurs in the catalyst layer on the anode side and the catalyst layer on the cathode side. As a result, hydrogen is discharged from the catalyst layer on the cathode side.

[0003] (Anode side) 2H2O→4H + +O2+4e -

[0004] (Cathode side) 2H + +2e - →H2

[0005] A conventional solid polymer water electrolysis device is described in, for example, Patent Document 1.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2022-023996 Summary of the invention

[0007] In conventional solid polymer water electrolysis devices, the entire catalyst layer is used as an electrode. However, if the entire catalyst layer is used as an electrode, if the accuracy of the catalyst layer relative to the formation range of the electrolyte membrane is low, the effective area that actually functions as an electrode will be biased.

[0008] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technology capable of suppressing variations in an effective region functioning as an electrode even if the accuracy of the formation range of a catalyst layer is low.

[0009] In order to solve the above-mentioned problems, the first invention of the present application is an electrode structure comprising: an electrolyte membrane; a first catalyst layer formed on one side of the electrolyte membrane; a first gas diffusion layer stacked on the surface of the first catalyst layer; a second catalyst layer formed on the other side of the electrolyte membrane; and a porous transport layer stacked on the surface of the second catalyst layer, wherein the outer peripheral edge of the porous transport layer is located at a position closer to the inside than the outer peripheral edge of the first gas diffusion layer, the outer peripheral edge of the first catalyst layer, and the outer peripheral edge of the second catalyst layer.

[0010] The second invention of the present application is an electrode structure according to the first invention, wherein the first catalyst layer and the second catalyst layer have an overlapping area that overlaps each other when observed along the stacking direction, and the outer peripheral edge of the first catalyst layer and the outer peripheral edge of the second catalyst layer are staggered, and the outer peripheral edge of the porous transport layer is located at a position closer to the inside than the outer peripheral edge of the overlapping area.

[0011] The third invention of the present application is an electrode structure according to the first or second invention, wherein, when observed along the stacking direction, the porous transport layer is rectangular, and the four sides of the porous transport layer are located at a position closer to the inside than the outer periphery of the first gas diffusion layer, the outer periphery of the first catalyst layer, and the outer periphery of the second catalyst layer.

[0012] A fourth invention of the present application is the electrode structure according to any one of the first to third inventions, wherein the first catalyst layer and the second catalyst layer are coating films.

[0013] According to the first to fourth inventions of the present application, the effective regions of the first and second catalyst layers are limited by the porous transport layer. Thus, even if the formation ranges of the first and second catalyst layers are low in accuracy, variations in the effective regions functioning as electrodes can be suppressed.

[0014] In particular, according to the second invention of the present application, regardless of the positional deviation between the first catalyst layer and the second catalyst layer, the effective regions of the first catalyst layer and the second catalyst layer can be limited by the porous transport layer.

[0015] In particular, according to the third invention of the present application, the rectangular effective regions of the first catalyst layer and the second catalyst layer can be defined with high accuracy using the porous transport layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of a water electrolysis device.

[0017] Figure 2 Schematic diagram of a cell unit and a pair of spacers located on both sides of the cell unit.

[0018] Figure 3 This is a diagram showing the electrode structure as viewed from the anode side in the stacking direction.

[0019] Figure 4 is a cross-sectional view of the electrode structure.

[0020] Description of Reference Numerals

[0021] 1. Water electrolysis device

[0022] 10 pool units

[0023] 20 Spacer

[0024] 30 cell stack

[0025] 40 Power Supply

[0026] 51 Electrolyte membrane

[0027] 61 first catalyst layer

[0028] 62First gas diffusion layer

[0029] 71 Second catalyst layer

[0030] 72Porous transport layer

[0031] 90 overlap area

[0032] AEffective Area DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0034] <1. Overview of water electrolysis device>

[0035] Figure 1 Schematic diagram of a water electrolysis device 1. The water electrolysis device 1 is a device for producing hydrogen by solid polymer water electrolysis. Figure 1 As shown, the water electrolysis device 1 has: a cell stack 30 including a plurality of cell cells 10 and a plurality of spacers 20; and a power source 40. The cell cells 10 and the spacers 20 are alternately stacked to form the cell stack 30. Hereinafter, the direction in which the cell cells 10 and the spacers 20 are stacked is referred to as the "stacking direction".

[0036] Figure 2 1 is a diagram schematically showing only one cell unit 10 in the cell unit stack 30 of the water electrolysis device 1 and a pair of spacers 20 located on both sides of the cell unit 10. Figure 2 As shown, one cell unit 10 includes an electrolyte membrane 51 , a first catalyst layer 61 , a first gas diffusion layer 62 , a second catalyst layer 71 , and a porous transport layer 72 .

[0037] The stacked body composed of the electrolyte membrane 51, the first catalyst layer 61, the first gas diffusion layer 62, the second catalyst layer 71 and the porous transport layer 72 is called a membrane electrode assembly (MEA). In addition, the stacked body composed of the electrolyte membrane 51, the first catalyst layer 61 and the second catalyst layer 71 is called a membrane catalyst layer assembly (CCM: Catalyst-coated membrane).

[0038] The electrolyte membrane 51 is a thin film (ion exchange membrane) having ion conductivity. The electrolyte membrane 51 of this embodiment conducts hydrogen ions (H + ) proton exchange membrane. A fluorine-based or hydrocarbon-based polymer electrolyte membrane is used as the electrolyte membrane 51. Specifically, for example, a polymer electrolyte membrane containing perfluorocarbon sulfonic acid is used as the electrolyte membrane 51. The membrane thickness of the electrolyte membrane 51 is, for example, 5 μm to 200 μm.

[0039] The first catalyst layer 61 is a catalyst layer that triggers an electrochemical reaction on the cathode side. The first catalyst layer 61 is formed on the surface of the cathode side of the electrolyte membrane 51. The first catalyst layer 61 includes a large number of carbon particles that support catalyst particles. The catalyst particles are, for example, platinum particles. However, the catalyst particles may be a material in which a small amount of ruthenium or cobalt particles are mixed with platinum particles. When the water electrolysis device 1 is used, hydrogen ions (H 2 ) are supplied to the first catalyst layer 61. + ) and electron (e - ). Then, a voltage is applied between the first catalyst layer 61 and the second catalyst layer 71 by using the power supply 40. In this way, under the action of the voltage and the catalyst particles, a reduction reaction occurs in the first catalyst layer 61, and hydrogen (H2) is generated from hydrogen ions and electrons.

[0040] The first gas diffusion layer 62 is used to transport electrons from the separator 20 to the first catalyst layer 61, and to transport hydrogen generated in the first catalyst layer 61 to the separator 20. The first gas diffusion layer 62 is stacked on the outer surface of the first catalyst layer 61 (the surface on the opposite side to the electrolyte membrane 51). The first catalyst layer 61 is sandwiched between the electrolyte membrane 51 and the first gas diffusion layer 62. The first gas diffusion layer 62 has electrical conductivity and is formed of a porous material. For example, a porous substrate (carbon paper) formed of carbon is used for the first gas diffusion layer 62.

[0041] The second catalyst layer 71 is a catalyst layer that triggers an electrochemical reaction on the anode side. The second catalyst layer 71 is formed on the surface of the anode side of the electrolyte membrane 51 (the surface on the opposite side to the first catalyst layer 61). The second catalyst layer 71 contains a large number of catalyst particles. Catalyst particles are, for example, iridium oxide (IrOx), platinum (Pt), an alloy of iridium (Ir) and ruthenium (Ru), an alloy of iridium (Ir) and titanium dioxide (TiO2), etc. When using the water electrolysis device 1, water (H2O) is supplied to the second catalyst layer 71. Then, a voltage is applied between the first catalyst layer 61 and the second catalyst layer 71 using the power supply 40. In this way, under the action of the voltage and the catalyst particles, water is electrolyzed into hydrogen ions (H + ), oxygen (O2) and electrons (e - ).

[0042] The porous transport layer 72 is used to uniformly supply water to the second catalyst layer 71 and to transport oxygen and electrons generated in the second catalyst layer 71 to the separator 20. The porous transport layer 72 is laminated on the outer surface of the second catalyst layer 71 (the surface on the opposite side of the electrolyte membrane 51). The second catalyst layer 71 is sandwiched between the electrolyte membrane 51 and the porous transport layer 72. The porous transport layer 72 has electrical conductivity and is formed of a porous material. For example, a porous substrate formed of a metal such as titanium or stainless steel is used for the porous transport layer 72.

[0043] The separator 20 allows electrons to move between adjacent cell units 10 and forms a passage for water, oxygen and hydrogen. The separator 20 is located between the first gas diffusion layer 62 and the porous transport layer 72 of the adjacent cell units 10. The separator 20 has electrical conductivity and is formed of a metal plate 21 that is impermeable to gas and liquid. The metal plate 21 has a cathode surface 22 in contact with the first gas diffusion layer 62 and an anode surface 23 in contact with the porous transport layer 72.

[0044] The cathode surface 22 of the metal plate 21 has a plurality of cathode grooves 24. The hydrogen gas generated in the first catalyst layer 61 passes through the first gas diffusion layer 62 and is discharged to the outside through the cathode grooves 24 of the separator 20.

[0045] The anode surface 23 of the metal plate 21 has a plurality of anode cells 25. Water is supplied to the porous transport layer 72 through the anode cells 25 of the separator 20. Oxygen generated in the second catalyst layer 71 passes through the porous transport layer 72 and is discharged to the outside through the anode cells 25 of the separator 20.

[0046] The power supply 40 is a device for applying voltage to the cell unit stack 30. Figure 1 As shown, the positive terminal of the power source 40 is electrically connected to the separator 20 at the end closest to the anode side of the battery cell stack 30. The negative terminal of the power source 40 is electrically connected to the separator 20 at the end closest to the cathode side of the battery cell stack 30. The power source 40 applies a voltage required for electrolyzing water to the battery cell stack 30.

[0047] When the water electrolysis device 1 is used, water is supplied from the anode tank 25 of the separator 20 to the second catalyst layer 71 via the porous transport layer 72. In this way, under the action of the voltage of the power supply 40 and the catalyst particles of the second catalyst layer 71, water is decomposed into hydrogen ions, oxygen and electrons. The hydrogen ions are transmitted to the first catalyst layer 61 through the electrolyte membrane 51. Oxygen is discharged to the outside through the porous transport layer 72 and the anode tank 25 of the separator 20. The electrons flow to the adjacent cell unit 10 through the porous transport layer 72 and the separator 20. In the adjacent cell unit 10, the electrons reach the first catalyst layer 61 through the first gas diffusion layer 62. Then, in the first catalyst layer 61, the hydrogen ions and the electrons are combined to generate hydrogen. The generated hydrogen is discharged to the outside through the first gas diffusion layer 62 and the cathode tank 24 of the separator 20. Thus, hydrogen is produced.

[0048] <2. Regarding the electrode structure>

[0049] As described above, the cell unit 10 is an “electrode structure” having a function as an electrode. Next, the structure of the cell unit 10 will be described in more detail. Figure 3 This is a diagram of one cell unit 10 as viewed from the anode side in the stacking direction. Figure 4 is a cross-sectional view of the cell unit 10 .

[0050] When viewed in the stacking direction, the electrolyte membrane 51, the first catalyst layer 61, the first gas diffusion layer 62, the second catalyst layer 71, and the porous transport layer 72 are all rectangular. Figure 4 As shown in FIG. 1 , the outer periphery of the first catalyst layer 61 is located further inward than the outer periphery of the electrolyte membrane 51. Therefore, when viewed in the stacking direction, the area of ​​the first catalyst layer 61 is smaller than the area of ​​the electrolyte membrane 51. Figure 4 As shown, the outer periphery of the second catalyst layer 71 is located inside the outer periphery of the electrolyte membrane 51. Therefore, the area of ​​the second catalyst layer 71 is smaller than the area of ​​the electrolyte membrane 51 when viewed in the stacking direction.

[0051] The first catalyst layer 61 is a coating film formed by coating a catalyst ink on one surface of the electrolyte membrane 51. The second catalyst layer 71 is a coating film formed by coating a catalyst ink on the other surface of the electrolyte membrane 51. When the catalyst ink is applied, the coating range is controlled so that the first catalyst layer 61 and the second catalyst layer 71 are in approximately the same position when viewed along the stacking direction. Therefore, when viewed along the stacking direction, the first catalyst layer 61 and the second catalyst layer 71 have an overlapping area 90 that overlaps with each other. However, it is extremely difficult to make the coating range of the catalyst ink on both sides of the electrolyte membrane 51 strictly consistent. Therefore, if Figure 4As shown, the position of the outer periphery of the first catalyst layer 61 is slightly offset from the position of the outer periphery of the second catalyst layer 71. In addition, when viewed in the stacking direction, the area of ​​the first catalyst layer 61 and the area of ​​the second catalyst layer 71 may not be exactly the same.

[0052] The first gas diffusion layer 62 is attached to the surface of the first catalyst layer 61 on the side opposite to the electrolyte membrane 51. The first gas diffusion layer 62 covers the first catalyst layer 61. The outer peripheral edge of the first gas diffusion layer 62 is located outside the outer peripheral edge of the first catalyst layer 61. The porous transport layer 72 is attached to the surface of the second catalyst layer 71 on the side opposite to the electrolyte membrane 51. The porous transport layer 72 covers a portion of the second catalyst layer 71. The outer peripheral edge of the porous transport layer 72 is located inside the outer peripheral edge of the second catalyst layer 71.

[0053] In such a cell unit 10 , a region where the first catalyst layer 61 , the first gas diffusion layer 62 , the second catalyst layer 71 , and the porous transport layer 72 overlap in the stacking direction forms an effective region A that substantially functions as an electrode.

[0054] In the case of the cell unit 10 of the present embodiment, the outer periphery of the porous transport layer 72 is located at a position further inside than the outer periphery of the first gas diffusion layer 62, the outer periphery of the first catalyst layer 61, and the outer periphery of the second catalyst layer 71. Therefore, in the present embodiment, the region of the porous transport layer 72 forms an effective region A that substantially functions as an electrode. That is, the effective region A of the first catalyst layer 61 and the second catalyst layer 71 can be defined by the porous transport layer 72. In this way, even if the accuracy of the formation range of the first catalyst layer 61 and the second catalyst layer 71 is low, the deviation of the effective region A that functions as an electrode can be suppressed.

[0055] In particular, when the first catalyst layer 61 and the second catalyst layer 71 are coating films, as described above, there is a slight misalignment between the position of the outer periphery of the first catalyst layer 61 and the position of the outer periphery of the second catalyst layer 71. However, in the present embodiment, the outer periphery of the porous transport layer 72 is located further inside than the outer periphery of the overlapping region 90 of the first catalyst layer 61 and the second catalyst layer 71. Therefore, regardless of the misalignment between the positions of the first catalyst layer 61 and the second catalyst layer 71, the effective region A of the first catalyst layer 61 and the second catalyst layer 71 can be defined by the porous transport layer 72.

[0056] In the present embodiment, the porous transport layer 72 has a rectangular shape when viewed in the stacking direction. In addition, the four sides of the outer periphery of the porous transport layer 72 are located inside the outer periphery of the first gas diffusion layer 62, the outer periphery of the first catalyst layer 61, and the outer periphery of the second catalyst layer 71. Therefore, the rectangular effective area A of the first catalyst layer 61 and the second catalyst layer 71 can be defined with high precision by the porous transport layer 72.

[0057] <3. Modifications>

[0058] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. Various modifications will be described below, centering on the differences from the above embodiment.

[0059] In the above embodiment, all four sides of the rectangular porous transport layer 72 are located inside the outer periphery of the first gas diffusion layer 62, the outer periphery of the first catalyst layer 61, and the outer periphery of the second catalyst layer 71. However, only a part of the four sides of the porous transport layer 72 may be located inside the outer periphery of the first gas diffusion layer 62, the outer periphery of the first catalyst layer 61, and the outer periphery of the second catalyst layer 71. For example, Figure 3 Of the two long sides and the two short sides of the porous transport layer 72 shown, only the two long sides or only the two short sides are located inside the outer periphery of the first gas diffusion layer 62 , the outer periphery of the first catalyst layer 61 , and the outer periphery of the second catalyst layer 71 .

[0060] In the above embodiment, the cell unit 10 using a proton exchange membrane as the electrolyte membrane 51 has been described. However, the electrode structure of the present invention may also use an anion exchange membrane as the electrolyte membrane.

[0061] In addition, the same structure as that of the above embodiment can also be used for an electrode structure used in a LOHC (Liquid Organic Hydrogen Carrier) process that produces an organic hydride (eg, toluene-methylcyclohexane) by hydrogenating an aromatic compound such as toluene.

[0062] Furthermore, part of the configuration of the above-described embodiment and modified examples may be deleted, or other configurations may be added without departing from the spirit of the present invention.

Claims

1. An electrode structure, comprising: Electrolyte membrane; a first catalyst layer formed on one surface of the electrolyte membrane; a first gas diffusion layer, stacked on a surface of the first catalyst layer; a second catalyst layer formed on the other side of the electrolyte membrane; as well as a porous transport layer, laminated on the surface of the second catalyst layer, The outer peripheral edge of the porous transport layer is located inside the outer peripheral edge of the first gas diffusion layer, the outer peripheral edge of the first catalyst layer, and the outer peripheral edge of the second catalyst layer.

2. The electrode structure according to claim 1, wherein: The first catalyst layer and the second catalyst layer have overlapping regions that overlap each other when viewed along the stacking direction, and the outer periphery of the first catalyst layer and the outer periphery of the second catalyst layer are offset from each other. The outer peripheral edge of the porous transport layer is located inside the outer peripheral edge of the overlapping region.

3. The electrode structure according to claim 1 or 2, wherein: The porous transport layer is rectangular when viewed in the stacking direction, and all four sides of the porous transport layer are located inside the outer periphery of the first gas diffusion layer, the first catalyst layer, and the second catalyst layer.

4. The electrode structure according to claim 1 or 2, wherein: The first catalyst layer and the second catalyst layer are coating membranes.

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